A study of the cutting forces and vibration characteristics in titanium machining

An investigation of titanium machining is presented in terms of cutting mechanics and dynamics.An experimental study examines the effects of the cutting parameters on the machining process of titanium alloy Ti6Al4V, as well as chatter vibration. The chip formation in near-orthogonal cutting transits from a mixture of serrated and continuous chips to completely serrated chips as the cutting speed increases. The feed has a profound effect on cutting forces and surface roughness, whereas the cutting speed and milling mode have indiscernible effect. Advanced signal processing techniques based on the improved HHT and SNEO are used to detect chatter. The original HHT is improved using EEMD and feature IMFs to highlight chatter characteristics. The experimental verification indicates that the improved HHT highlights the dynamic transitions at chatter onset, and the energy ratio tracks the instantaneous energy change.A predictive force model is developed for orthogonal cutting, which models the material flow stress using the Johnson-Cook material law and considers a thermal model with non-uniform heat partitions at the tool-chip interface. The model is verified with experimental data, which shows the capability to predict the average values of the experimental force and chip thickness with considerable accuracy. Comparisons of the predicted temperatures against the simulated temperatures from finite element method show that the predicted maximum temperatures agree well with those from the finite element method. Moreover, the predictive force model is extended to the milling process. A stability analysis is conducted to predict the stability diagram. The tool tip FRF is obtained through receptance coupling which overcomes unavailability of impact testing when the tool diameter is small. Two stability analysis methods, Chebyshev collocation and time domain simulation, are applied to solve the system dynamic equation. Comparisons of the two methods against the experimental results reveal that the time domain simulation method performs better in chatter prediction. The effects of the helix angle and workpiece dynamics on stability are discussed. It is found that a non-zero helix angle improves the stability limit. The workpiece dynamics should be included if a flexible workpiece is machined